Stable-surface alloy steel.



UNITED STATES PATENT OFFICE.

PER-CY A. E. ARMSTRONG, OF LOUDONVILLE, NEW YORK.

STABLE-SURFACE ALLOY STEEL.

No Drawing.

To all whom it may concern:

Be it known that I, PERCY A. E. ARM- s'rnonc, a subject of the King of Great Britain, and residing at Loudonville, in the county of Albany, State of New York, have invented certain new and useful Improvements' in Stable-Surface .Alloy Steel, of which the following is a specification.

My invention relates to an alloy steel containing iron, silicon, chromium and carbon, and ofa highly stable character, that is to say, highly resistant to change or deterioraalloy well together and a Streaky and irregular effect is likely to be produced,

articles made from the same melt often differing widely in their qualities. Ironchromium alloys have a tendenc toward red shortness with resulting crac s, blemishes and fissures, and scale bad] when heated to temperatures required for ot mechanical working during commercial operations. The quantity ofcarbon which can be present in iron-chromium alloys without causing .very substantial loss of surface stability or resistance to deterioration is quite limited. With my improved alloy steel, difiicnlties of this character are either absent or are "reduced to the minimum.

Without being limited to any particular .theory of the action'of silicon in the alloy, I

believe that the very excellent character of the material obtained by my invention may be accounted for by the formation of a silicid or silicids of iron, and of a silicid or silicids' of chromium, which iron and chromium silicids are miscible with one another when molten. In any event, the silicon acts as a third alloy material which is highly beneficial in bringing about the formation of a substantially homogeneous alloy, free from Specification of Letters Patent.

. u a lag or retardation to chan Patented Nov. 25, 1919.

Application filed May 24, 1919. Serial No. 299,688.

troublesome streaks and irregularities, of high surface stability and readily workable, This beneficial action of silicon is not appreciabl'e where it is present only in small proportions, say up to 30-40%. To gt such beneficial efiects at least .5070 of silicon must be present and more silicon is desirable. With the use of silicon as described herein, it becomes possible to have the ground mass of the material substantlally solid solution. The more the ground mass is solid solution, the greater appears to be the stability of the allo steel produced. With the silicon in the al 0y steel, greater amounts of carbon can be used than would be available for production of stable surface material without a substantial proportion of silicon.

I believe that the action of carbon is one of fixing or, in other words, one of' setting in the a loy steel during cooling, and further that the carbon enters into combination with the iron and chromium, which combinations, however, re modified by the action ofthe silicon present.

With my new alloy steel large numbers of small areas, of appearance, similar tocarbids in straight carbon steel, may be distinguished underthe microscope and, while -I have been unable to isolate same, I am inclined to consider them to be {chromium car-bids, though they may be mere concentrations of the ground mass fixed in their Proportions given herein are by weight and it is to be noted that the atomic weight of silicon being only about half of that of chromium or 1ron,-the percentages of this component, if stated by yolume, would be about twice the figures g1ven.herein.'

For production of stable surface material to be subjected to mechanical working, the silicon content may be from about 50% to 8%, and the chromium from about 3% to sci ing worked mechanically,

1 .25 stud solution ground mass.

7 so iWith such as silicon and chromium, taken together.

a. say 1%,

"getter,

Qthe ground mass and has high 5:0 l ility' w j g, such chromium may be increased, without substantially together, from about 5% to about 58%. Mechanical workabilitybecoines very slight as the extreme upper hunts stated are ap- 5 proached, but with up to about -30% of chromium and about 5-6% of silicon the material can be hot forged reasonably well.

The material just described may be cast, in

fact, it usually is cast into ingots before beand castings may be made therefrom if desired. For making castings, however, which are not to be mechanically worked, more silicon may be used up to" about and chromium up to about or even higher.

The alloy steel having over about 5% and under about 13% silicon and chromium, taken together, is practically stainless and 1s resistant to corrosion and the like, when the 20 ground mass is fixed solid solution by heattreatfient, but is more or less readily attacireilbycorroding and the like agents when not in such state. Heat-treatment is necessary with this material in order to obtain For production of. such material the silicon may be from 5% to 7%, and chromium 3% to 10%, the prO- portions being distributed between the two so as to keep the totals between 5% and 13%. 1 low proportions of silicon and chromium, taken together, the carbon should i be kept low to get good results. Carbon as I lo;v1as..05% may be used. Preferably the carbonshould be kept under one-tenth of With analloy steel containing silicon 2.5% and chrnmiunr'a7c, for example, the carbon shoiildpreferably be under since, with suntan-anal, further increase of carbon, to 7 results in a considerablereduction of the desired surface stability in the alloy steel. 7 Carbon 30%, for example, gives good results with these proportions of silicon and chromium, provided the ground mass 13 15 fixed solid solution by heat-treatment.

, lYith chromium and silicon, taken to- 7 over 13%, and chromium over 10%, the material is substantially solid solution in surface stawhether heat-treated or not. \Vith I V and silicon, the carbon conreducing the desirable qualities of the mate- "rial, as, for example, with chromium about 55 10. to; 20%, and silicon about 2% to 7%. it I "'is'sufiicicnt, so long as a maximum 0 gearbon is not exceeded, to keep the carbon :b elow one-sixth of silicon and chromium,

taken together. For example, one very good -13, and carbon t'jiiorkable material is desired, low carbon down to about 05??) may be used and in sucltcase the silicon may be less, down to r to alloy steel containsrhrominm 13.7%, silicon If more readily 5 about .5 ,7;

1% gives good results.

' bon tends to make the material brittle and dillicult to work, if the silicon is low. Such material is readily workable, however, if the silicon is more than twice the carbon, up to about 8% of silicon. For example, an alloy steel having chromium 22%, silicon 4.5%, and carbon 2.1% has high service stability and works well. As before, 3.5% carbon is about the maximum for mechanically work able material. Considerable relative reduction in carbon is permissible, if desired, as, for example, another good alloy steel contains chromium 31%, silicon 6.12%, and carbon 138%.

As already stated the alloy steel, when used for making castings not mechanically worked, may contain up to about chromium, and up to about 30% silicon. The carbon in such cast material should preferably be less than one-half the silicon.

With the silicon-chromium content about 13% or over, the alloy is highly resistant to change or deterioration in the hot state. Cast into ingots it forges and rolls with very noticeable absence of mill scale, and when rolled down has practically nothing but a-sort of brownish rouge on the surface, of extreme thinness. When exposed to an oxidizing atmosphere at about 1800 F. for over a month, a specimen containing about 12% chromium, 5% silicon and .45% carbon, showed no more than surface dark ening. Alloy steel of this composition does not melt until heated to about 2600 F., and this specimen had a specific resistance of 115 microhms per cubic centimeter. Such material, and material having still higher silicon-chromium content is well adapted for electrical heating elements, particularly where run at high temperatures, which may be as great as 18002000 F. or even higher, the temperatures permissible depending to some extent, at least, upon the times they are maintained. For electrical heating elements where lower temperatures are suflicient, say 1300 F. or so, the material may have less silicon-chromium content, so-long as silicon and chromium, taken together, are ovcr5%. The specific resistance of an alloy steel of about this proportion is about microhms. The specific resistance increases much more rapidly with increase of silicon than with increase of chromium, The cast material as well as the mechanically worked material may be made use of for electrical heating elements. When the production of electrical heating elements involves a drawing or bending operation the carbon should be kept low, for example, under 13% of chromium and silicon taken together. carbon may desirably be about .40? and for over 13% siliconchromium content, carbon about. Higher carbon may which is expensive to produce. I have found that silicon may be used as a good and in- .expensive reducing agent in preparingthe considerable extent into the molten metal as to good advantage.

ferro-chromium for my alloy steel. Silicon, when used as a reducing agent, enters to a an alloy component, and in this way a ferrochromiumsilicon alloy may be cheaply and conveniently produced. The ferrous alloy so obtained, may be made use of directly in the melting furnace, with, of course, the addition of other materials for obtaining the proper proportions of the various alloy componen and various grades of ferrogchromium silicon may be utilized by proper choice of other materials. In this way the process of manufacture is simplified and a considerable saving effected of valuable materials, including chromium and silicon. From to nearly 100% of the silicon and practically all the chromium used in the melt can be gotten in the finished product, particularly when the melting is done in the electric furnace, which I consider the desirable apparatus for the purpose, though other systems of melting may be used, if desired, and materials from other sources may, of course, be used.

The known silicids, especiall the chromium silicids, can be used to a vantage as a ready guide to the production of good quality alloy steel and the nearer the composition is to that of the known silicids the bet ter appears to be its surface stability:

My new material has quite distinctive cooling and heating curves, showing two marked transformation points or stages,the upper one of which tends to rise with increase of silicon and chromium content, or with increase of silicon content alone.

The material has a long; plastic stage when melted and cast into an ingot or other mold; with small molds it readily solidifies into coherent ingots which can be worked When cast into larger molds the period of solidification is quite long unless provision is made for withdrawing the heat fairly rapidly. When means are not resorted to to keep down the time for solidification. the casting may be done bv top pouring of the metal from the ladle with a considerable proportion of slag which forms a protecting envelop all around and over the molten metal, and can be readily knocked off. when the ingot has been re stage has the valuable property of eliminatmg pipe in properly cast ingots or other castings to a ve large degree and it is useful, particular y in making small castings, for readily producing castings of great soundness. The plastic stage is likewise quite long upon heating. This long plastic sta e can be utilized to good advantage in ma ing various articles and shapes from my new alloy steel, as, for example, it may be extruded or press or drop formed into pipes, bars and shapes of various kinds.

An important property of my new alloy steel is its high resistance to rapid heating or cooling. Placed in a furnace with apiece of ordinary carbon steel, for example, of like dimensions, it remains black for some time after the ordinary steel has been heated to a yellow heat. When made use of' forgun linings and the like, where the surface is subjected to the action of nitrous vapors at extremely hi h temperatures for short periods, highly heat and cool rapidly, this material gives extremely good results and is highly resistant to erosion. By reason of this same characteristic it is well adapted for a variety of important uses, such as annealing tubes, boxes and articles which are subjected to varying temperatures over long periods. This valuable property of slow heating enables the charge in the annealing boxes and the like to be more uniformly heated than is possible with the alloys or mdtals at present employed for such purposes. 7

My improved alloy has the important property of not being readily permeable to gases at high temperatures and is, therefore, well adapted for apparatus such as containers for highly heated gases being sub jected to chemical reaction, and for use in tubes for protecting thermo couples of pyrometeis, and the like, where it is important to shield highly heated metallic material from being corroded by attacking gases.

The new alloy material. especially when it contains above 13% silicon and chromium taken together, is not attacked or stained to any perceptible extent by nitric acid, nor by acetic or other organic acids, fruit juices and the like. It is attackedto some extent, however, by hydrochloric acid, sulfuric acid,

destructive of materials which and hydrofluoric acid, particularly when diluted.

My improved alloy steel, containing substantial proportions of silicon, has'greater surface stability, that is to say, is much more resistant to stain, oxidation, corrosion and the like, than similar materials not containing a substantial proportion of silicon. Ingots and billets, made from my alloy are worked with practically no formation of mill scale whatever, w ereas materialof analysis similar to my alloy steel, but containing no silicon more than a very small percentage, for instance. 3%,: whcn heated for hot mechanical working, will scale very badly. So extremely resistant is my alloysteel to}oxidationi that when carbon analysis is being run, y passing oxygen thereover in presence 0 high heat, it

so has been found impossible to get the carbon out by combustion withoutthe addition of oxid, such as lead oxid, so as to set up a chemical action upon the carbon, whereas with an alloy containing the same amount of chromium as my material, but with little so" The alloy steel sex like. As an instance of inch bar mill down to a as; 4.5% andcutlery or no silicon, an accurate determination of carbon by oxygen can be readily. made without resort to use of foreign oxide or the like.

of my invention, within the ranges given for mechanical working above, can be readily worked and is not red short, and is remarkably from troublesome cracks, iissmres, blemishes,

its remarkable freedom'from surface seams, a 7 inch ingot heat ed to the necessary to rature for rolling, was cogged, down: in an- 1-8 inch mill in the billet form, then reheated and rolled in a 9 inch round bar,

free omcracks, and

jA-12 inch square ingot, cast with an envelop of slag, and containing chromium about 17%, silicon about carbon about .8% wasfforged under' a steam hammer out into billets and rolled downto a inch square bar, with similarly good results. Such good results are very diflicult to obtain, even from low and; was entirely seams ofany sort.

* carbon steel free fromalloys, and impossible to obtain from steel containing any such pemntage' of chromium, with no more than 30% of silicon and with such high carbon. Some-of the uses of my improved alloy material have already been reicrred to, in-

cluding electrical heating units, castings,

and tools, gun in tubes, etc. My alloy steel is eminently suitable for a variety of other uses, including laundry machinery, propellers, water pipes and pumps for fresh and salt water, for refri erator pipes and fittings, and generally or apparatus; fittings, etc, which are exposed to heat, moisture, steam or intense cold; -for apparatus and too 5, steel rules, articles and thengs, annealing esa-am articles exposed to action of alkalis to which the alloy steel is highly resistant, also for objects exposed to the atmosphere, such as hinges, latches, and outside hardware generally, for electrical fittings, 'for power transmission, electric trolley or railroad service, particularly those parts that have to withstand electrolysis, balls for water valves, ball bearing balls and races for ball bearings which haveto work under water, shi fittings, surgical instruments, dental for personal wear, such as jewelry settings, coins and medals; automatic stoker bars which have to with stand high temperatures, and very many. other purposes where high resistance to stain, oxidation and corrosion are required. The alloy steel has low magnetic hysteresis and by suitable heat-treatment can be made substantially non magnetic. These qualities make it available for many additional uses, such as in scientific instruments, electrical meters and the like.

My improved alloy steel, of course, contains small percentages of metalloids, such as sulfur, pros horous, arsenic, etc, and may contain variab e ercentages of metallic elements substantia ly all of which can be employed, to some extent, at least. If the chromium-silicon content is high the quantity of metallic elements which may be present without substantial detriment to this surface stability of the alloy steel may be correspondin ly increased. It is undesir able, ordinarily, to include any of these metallic elements in percentages over 1%, when the total chromium and silicon used is as low as 5%, but when 13% or more of vchromium and silicon is used, other metallic elements can be incor orated up to a total of about 2% to 5% without substantial detriment to the valuable properties of my allo steel. I may, for example, incorporate with the all steel having chromium-silicon content 0 13 or over, as much as 4% of cobalt or nickel, 1% of manganese,

molybdenum, tungsten vanadium, titanium, zirconium, or other metals which form silicids or compounds or alloys with the iron, or chromium or both, or which do not materiall efiect the solid solution ground mass, wit no considerable-detriment resulting from their use.

I claimi 1. An alloy steel of high surface stability containing chromium 3% to 50%, carbon .05% to 3.5% but not more than of chromium and silicon taken together up to about 13% thereof and not more than 1/6 thereof above about 13%, silicon under 8%, over .5% and also over twice the-carbon, silicon and chromium together 5% to 58%, and the principal portion of the remainder iron.

2. Am alloy steel of high surface stability containing chromium over 10%, carbon over 05% silicon over .5% chromium and silicon together over 13%, and the principal portion of the remainder iron.

3. An alloy steel of high surface stability containing chromium over 10%, carbon over .05%, silicon over .5% and also over twice the carbon, chromium and silicon together over 13%, and the principal portion of the remainder iron.

4. An allo steel of high surface stability, containing romium 10% to 20%, silicon .5% to 8%, chromium and silicon together 13%. to 28%, carbon over under 3.5%, and also under 1/6 of chromium and silicon taken together, and the principal portion of the remainder iron.

5. An allo steel of high surface stability, containing chromium over carbon over .05%, and more than twice as much silicon as carbon, and the remainder iron.

6. An alloy steel of high containing chromium 3% .05% to 3.5%, silicon .5% twice the carbon, and the of the remainder iron. i

7. A cast article of high surface stability composed of an alloy steel containing chromium 3% to 60%, carbon over .05%' silicon .5% to 30% and more than twice the carbon, and the principal portion of the re mainder iron.

In testifnony that I claim the foregoing I hereto set my hand, this 22nd day of May, 1919.

principal portion of the surface stability, to carbon to 8% and over principal portion PERCY A. E. ARMSTRONG.

It is hereby certified that' inTJetiiera Patent No. 1,322,511, granted November 25, 1919, upon the application of Percy A. E. Armstrong, of Loudonville, New York,

'for an improvement in Stable-Surf ace Alloy Steel, an error appears in the printed specification requiring correction as follows: Page 4, 14, or for instance. read for instmwe 3% the space occurring between the word instance" and the period; and that the said Letters Patent should;be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 13th day of January, A. D.; 1920.

M. H. COULSTON,

Acting Commissioner of Patents.

D1SCLAIME R.- 1,322.51L-Perc A. E. Armstrong, Loudonville, N. Y. Swarm-Swarm: ALI-DY 5111111.. Patent dated November 25, 1919. Disclaimer filed January 3, 1928, by the patentee and the assignee, udZu m. Steel Company.

Hereby enter this disclaimer to such parts of the thing patented as they do not choose to claim or to hold by virtue of the atent. and assignment, to Wlt, such parts oi. the specification and of each claim of 't a patent except claim 4 es inclu e matenals or articles containing over 20% of chrominm or over 8% of sihcou.

[Ofleial Gazette January 17, 1928.] 

